Software Engineering Demo for a K-5 Career Fair?

gmjohnston asks: "A local elementary school is having a Career Fair in a couple of weeks and I volunteered. The idea is for parents with various jobs and careers to show and tell the kids a little bit about what their's is, why they think it's interesting and rewarding, etc. It's to try to give kids a little early exposure to some of the diverse kinds of things one can do with one's life. I'm a software engineer, so I'd like to show something that has to do with programming or Computer Science, but which would be interesting to an elementary school student." What would be the best way to illustrate what a software engineer does to a group of primary school kids? "I'm trying to come up with something like what got me hooked way back when, which was when my Organic Chemistry professor in college showed me a listing of a Basic program (Basic Plus on a PDP-11/70 running RSTS/E if you must know) and I realized that, computers relied on a bunch of instructions that tell the machine what to do, and that if I could change the instructions then I could make the machine do what *I* want it to do! I'll have my laptop with me and I'll be at a table that the kids will be able to gather around and see the screen (or potentially do something themselves on the laptop, depending on what I come up with). Of course, showing them the kind of code I really work on (software development tools) would likely instantly bore them to death. So, the question is: What should I show? If other Slashdot readers have done this kind of thing, what did you do and how did it work out?"